Doped Organic Semiconductors and Methods of Making the Same

The present application claims priority to U.S. Provisional Application No. 63/170,085, filed Apr. 2, 2021, which is incorporated by reference herein in its entirety.

This invention was made with government support under Grant No. CBET-0954985, awarded by the National Science Foundation, and by Contract No. DE-SC0012704, awarded by the Department of Energy. The Government has certain rights in the invention.

Doping is key in leveraging control of the electrical properties of semiconductors (Chiang, C. K. et al. Phys Rev Lett 1977, 39, 1098-1101; Macdiarmid, A. G. & Heeger, A. J. Synthetic Met 1980, 1, 101-118; Macdiarmid, A. G. & Heeger, A. J. Synthetic Met 1980, 1, 101-118), as it governs the essential parameters in their electronic applications (Blochwitz, J., et al., Appl Phys Lett 1998, 73, 729-731; Walzer, K., et al., Chem Rev 2007, 107, 1233-1271; Yim, K. H. et al. Adv Mater 2008, 20, 3319; Zhang, Y., et al., Adv Funct Mater 2009, 19, 1901-1905; Yurash, B. et al. Nat Mater 2019, 18, 1327-1334). In perovskite solar cells, organic semiconductors are often used as essential interlayers between the photoactive layer and the electrodes. Their electrical properties significantly affect charge collection efficiencies and therefore determine the overall device performance (Cho, A. N. & Park, N. G. Chemsuschem 2017, 10, 3687-3704; Zhang, W. X. et al. Adv Sci 2018, 5, 1800159). 2,2′,7,7′-Tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9-spirobifluorene (spiro-OMeTAD), a π-conjugated small molecule, is the most commonly used semiconductor for the hole-conducting layer (Hawash, Z., et al., Adv Mater Interfaces 2018, 5, 1700623; Bach, U. et al. Nature 1998, 395, 583-585; Green, M. A., et al. Nat Photonics 2014, 8, 506-514; Tan, H. R. et al. Science 2017, 355, 722-726; Saliba, M. et al. Energ Environ Sci 2016, 9, 1989-1997; Lee, C. P., et al., Mater Today 2017, 20, 267-283). To enhance the electrical conductivity of spiro-OMeTAD, lithium bis(trifluoromethane)sulfonimide (LiTFSI) is typically employed for a doping process that is conventionally initiated by exposing the spiro-OMeTAD:LiTFSI blend films to air and light for several hours, with oxygen acting as the p-type dopant (Cappel, et al.,2012, 12, 4925-4931; Abate, A. et al. Phys Chem Chem Phys 2013, 15, 2572-2579; Wang, S., et al., Acs Appl Mater Inter 2015, 7, 24791-24798; Nguyen, W. H., et al., J Am Chem Soc 2014, 136, 10996-11001). This time-costly process largely depends on ambient conditions and is a hindrance to the commercialization of perovskite solar cells.

There remains a need in the art for improved methods of doping semiconductors. The present invention addresses this unmet need.

In one aspect, the present invention relates to a composition comprising an organic semiconductor; and a metal salt having the formula MX; wherein Xis a monoanionic species; and wherein the ratio of Mto Xin the hole transport material is less than about 1.00. In one embodiment, the metal salt is LiTFSI, LiPFSI, or LiPF. In one embodiment, the organic semiconductor comprises spiro-OMeTAD or a derivative thereof.

In another aspect, the present invention relates to a composition comprising an organic semiconductor; a metal salt having the formula MXwherein Xis a monoanionic species; and a metal carbonate having the formula MCO; wherein the metal of the carbonate and the metal of the metal salt are the same; and wherein the total metal content of the composition is approximately equal to the Xcontent of the composition. In one embodiment, the organic semiconductor comprises a semiconducting polymer selected from the group consisting of poly(3-hexylthiophene)(P3HT), poly[(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)-benzo[1,2-b:4,5-b′]dithiophene))-alt-(5,5-(1′,3′-di-2-thienyl-5′,7′-bis(2-ethylhexyl)benzo[1′,2′-c:4′,5′-c′]dithiophene-4,8-dione)])(PBDB-T), poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA), and poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene](MEH-PPV). In one embodiment, the metal salt is LiTFSI, LiPFSI, or LiPF.

In another aspect, the present invention relates to a method of producing a doped organic semiconductor, the method comprising the steps of providing an organic semiconductor solution; contacting the organic semiconductor solution with CO; and irradiating the organic semiconductor solution with ultraviolet light. In one embodiment, the method further comprises the step of removing at least one precipitate from the organic semiconductor solution. In one embodiment, the method further comprises the step of isolating a mixture of the organic semiconductor and a doped organic semiconductor from the organic semiconductor solution. In one embodiment, the precipitate comprises MCO.

In one embodiment, the step of contacting the organic semiconductor with COcomprises the step of bubbling COthrough the organic semiconductor solution. In one embodiment, the step of contacting the organic semiconductor with COoccurs simultaneously with the step of irradiating the organic semiconductor solution with ultraviolet light.

In one embodiment, the organic semiconductor solution comprises at least one organic semiconductor. In one embodiment, the organic semiconductor solution comprises spiro-OMeTAD or a derivative thereof. In one embodiment, the organic semiconductor solution comprises a semiconducting polymer. In one embodiment, the semiconducting polymer is selected from the group consisting of poly(3-hexylthiophene)(P3HT), poly[(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)-benzo[1,2-b:4,5-b′]dithiophene))-alt-(5,5-(1′,3′-di-2-thienyl-5′,7′-bis(2-ethylhexyl)benzo[1′,2′-c:4′,5′-c′]dithiophene-4,8-dione)])(PBDB-T), poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine](PTAA), and poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene](MEH-PPV). In one embodiment, the organic semiconductor solution comprises LiTFSI.

In another aspect, the present invention relates to doped organic semiconductor material produced using the methods described herein, as well as hole transport layer comprising the doped organic semiconductor material and a photovoltaic device comprising the doped organic semiconductor material.

It is to be understood that the figures and descriptions of the present invention have been simplified to illustrate elements that are relevant for a clear understanding of the present invention, while eliminating, for the purpose of clarity, many other elements found in photovoltaic devices. Those of ordinary skill in the art may recognize that other elements and/or steps are desirable and/or required in implementing the present invention. However, because such elements and steps are well known in the art, and because they do not facilitate a better understanding of the present invention, a discussion of such elements and steps is not provided herein. The disclosure herein is directed to all such variations and modifications to such elements and methods known to those skilled in the art.

As used herein, each of the following terms has the meaning associated with it in this section. Unless defined otherwise, all technical and scientific terms used herein generally have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

The articles “a” and “an” are used herein to refer to one or to more than one (i.e. to at least one) of the grammatical object of the article. By way of example, “an element” means one element or more than one element.

As used herein, the term “about” will be understood by persons of ordinary skill in the art and will vary to some extent depending on the context in which it is used. As used herein when referring to a measurable value such as an amount, a temporal duration, and the like, the term “about” is meant to encompass variations of ±20% or ±10%, more preferably ±5%, even more preferably ±1%, and still more preferably ±0.1% from the specified value, as such variations are appropriate to perform the disclosed methods.

As used herein, the terms “electrode” and “contact” may refer to a layer that provides a medium for delivering current to an external circuit or providing a bias current or voltage to the device. For example, an electrode, or contact, may provide the interface between the active regions of an organic photosensitive optoelectronic device and a wire, lead, trace or other means for transporting the charge carriers to or from the external circuit. Examples of electrodes include anodes and cathodes, which may be used in a photosensitive optoelectronic device.

As used herein, the term “transparent” may refer to a material that permits at least 50% of the incident electromagnetic radiation in relevant wavelengths to be transmitted through it. In a photosensitive optoelectronic device, it may be desirable to allow the maximum amount of ambient electromagnetic radiation from the device exterior to be admitted to the photoconductive active interior region. That is, the electromagnetic radiation must reach a photoconductive layer(s), where it can be converted to electricity by photoconductive absorption. This often dictates that at least one of the electrical contacts or electrodes should be minimally absorbing and minimally reflecting of the incident electromagnetic radiation. In some cases, such a contact should be transparent or at least semi-transparent. In one embodiment, the transparent material may form at least part of an electrical contact or electrode.

As used herein, the term “semi-transparent” may refer to a material that permits some, but less than 50% transmission of ambient electromagnetic radiation in relevant wavelengths. Where a transparent or semi-transparent electrode is used, the opposing electrode may be a reflective material so that light which has passed through the cell without being absorbed is back reflected through the cell.

As used and depicted herein, a “layer” refers to a member or component of a device, for example an optoelectronic device, being principally defined by a thickness, for example in relation to other neighboring layers, and extending outward in length and width. It should be understood that the term “layer” is not necessarily limited to single layers or sheets of materials. In addition, it should be understood that the surfaces of certain layers, including the interface(s) of such layers with other material(s) or layers(s), may be imperfect, wherein said surfaces represent an interpenetrating, entangled or convoluted network with other material(s) or layer(s). Similarly, it should also be understood that a layer may be discontinuous, such that the continuity of said layer along the length and width may be disturbed or otherwise interrupted by other layer(s) or material(s).

As used herein, a “photoactive region” refers to a region of a device that absorbs electromagnetic radiation to generate excitons. Similarly, a layer is “photoactive” if it absorbs electromagnetic radiation to generate excitons. The excitons may dissociate into an electron and a hole in order to generate an electrical current.

As used herein, “spin coating” may refer to the process of solution depositing a layer or film of one material (i.e., the coating material) on a surface of an adjacent substrate or layer of material. The spin coating process may include applying a small amount of the coating material on the center of the substrate, which is either spinning at low speed or not spinning at all. The substrate is then rotated at high speed in order to spread the coating material by centrifugal force. Rotation is continued while the fluid spins off the edges of the substrate, until the desired thickness of the film is achieved. The applied solvent is usually volatile, and simultaneously evaporates. Therefore, the higher the angular speed of spinning, the thinner the film. The thickness of the film also depends on the viscosity and concentration of the solution and the solvent.

As used herein, the term “substrate” refers to a structural surface beneath or above a layered material or coating (e.g., glass or polymer coating). In one embodiment, substrate materials can be used for encapsulation of devices. In one embodiment, special encapsulants can be also used to project devices from degradation such as oxygen transmission and moisture ingress.

As used herein, the term “spiro-OMeTAD” refers to 2,2′,7,7′-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9-spirobifluorene.

As used herein, the term “Li-TFSI” or “LiTFSI” refers to lithium bis(trifluoromethane)sulfonimide.

As used herein, the term “TFSI-” refers to the bis(trifluoromethane)sulfonimide anion.

As used herein, the term “tBP” refers to 4-tert-butylpyridine.

Throughout this disclosure, various aspects of the invention can be presented in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the invention. Accordingly, the description of a range should be considered to have specifically disclosed all the possible sub-ranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 2.7, 3, 4, 5, 5.3, and 6. This applies regardless of the breadth of the range.

The present invention is based in part on the unexpected discovery that bubbling a semiconductor in solution with COunder light promotes p-doping of the semiconductor solution and improves conductivity of the resulting film.

In one aspect, the present invention relates to a method of producing a doped organic semiconductor. Exemplary methodis depicted in. In step, an organic semiconductor solution is provided. In step, the organic semiconductor solution is contacted with CO. In step, the organic semiconductor solution is irradiated with ultraviolet light. In some embodiments, stepand stepare performed simultaneously.

In one embodiment, the organic semiconductor solution comprises at least one small molecule semiconductor. In one embodiment, the organic semiconductor solution comprises spiro-OMeTAD. In one embodiment, the organic semiconductor solution further comprises t-butyl pyridine (tBP). However, the organic semiconductor solution is not limited to these components and may include any material known those of skill in the art.

In one embodiment, the organic semiconductor comprises at least one electrolyte or metal salt. In one embodiment, the organic semiconductor comprises at least one metal salt having the formula MXwherein M is a monocationic metal, such as an alkali metal, transition metal, rare earth metal, post-transition metal, or metalloid and Xis a monoanionic organic species. Contemplated alkali metals include lithium, sodium, potassium, rubidium, and cesium. Contemplated alkaline metals include beryllium, magnesium, calcium, strontium, and barium. Exemplary transition metals include, but are not limited to, scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, yttrium, zirconium, niobium, molybdenum, technetium, ruthenium, rhodium, palladium, silver, cadmium, hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold, and mercury. Exemplary post-transition metals include aluminum, gallium, indium, tin, thallium, lead, and bismuth. Exemplary metalloids include boron, silicon, germanium, arsenic, antimony, and tellurium. Exemplary rare earth elements include lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium.

In one embodiment, the electrolyte comprises a lithium salt. In one embodiment, the lithium salt comprises a compound having the formula LiX, where X is a monoanionic species. In one embodiment, the electrolyte comprises a sodium salt. In one embodiment, the sodium salt comprises a compound having the formula NaX, where X is a monoanionic species. In one embodiment, the electrolyte comprises a silver salt. In one embodiment, the silver salt comprises a compound having the formula AgX. In one embodiment, the electrolyte comprises a copper salt. In one embodiment, the copper salt comprises a compound having the formula CuX. In one embodiment, the electrolyte comprises an organic cation.

Exemplary monoanionic species X include, but are not limited to, hexafluorophosphate (PF), tetrafluoroborate (BF), hexafluoroarsenate (AsF), perchlorate (ClO), bis(trifluoromethylsulfonyl)imide[(SOCF)N]), bis(perfluoroethylsulfonyl) imide[(SOCF)N]), trifluoromethanesulfonate (CFSO), nonafluorobutanesulfonate (CFSO), difluoro oxalato borate anion (BF(CO)), cyclo-hexafluoropropane-1,3-bis(sulfonyl)imide (NSOCFSO), bis(fluorosulfonyl)imide ((SOF)N), fluoroalkyl-phosphates, and the like.

Exemplary electrolytes include, but are not limited to, lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF), lithium hexafluoroarsenate (LiAsF), lithium perchlorate (LiClO), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium bis(perfluoroethylsulfonyl)imide (LiN(CFSO)), lithium trifluorosulfonate (CFSOLi), lithium nonafluorobutanesulfonate, lithium difluoro oxalato borate anion (LiDFOB), lithium bis(oxalato)borate (LiBOB), lithium cyclo-hexafluoropropane-1,3-bis(sulfonyl)imide, sodium bis(fluorosulfonyl)imide (NaFSI), sodium bis(trifluoromethylsulfonyl)imide (NaTFSI), sodium bis(pentafluoroethanesulfonyl)imide (NaBETI), Li-Fluoroalkyl-Phosphates (LiPF(CFCF)), and the like. In one embodiment, the organic semiconductor solution further comprises a cobalt salt, such as FK209 Co(III)TFSI salt, FK209 Co(III) PFsalt, FK102 Co(III)TFSI salt, or FK102 Co(III) PFsalt.

In one embodiment, the electrolyte is present in excess. In one embodiment, the ratio of electrolyte to small molecule conductor in the organic semiconductor solution is between about 100:1 and about 1:100. In one embodiment, the ratio of electrolyte to small molecule conductor is greater than or equal to about 1:10, 1:9, 1:8, 1:7, 1:6, 1:5, 1:4, 1:3, 1:2, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, or 10:1.

In one embodiment, the organic semiconductor solution comprises a semiconducting polymer. Exemplary semiconducting polymer classes include, but are not limited to, poly(fluorene)s, polyphenylenes, polypyrenes, polyazulenes, polynaphthalenes, poly(pyrrole)s, polycarbazoles, polyindoles, polyazepines, polyanilines, poly(thiophene)s, poly(p-phenylene sulfide)s, poly(acetylene)s, or poly(p-phenylene vinylene)s, benzothiadiazole, or any combination thereof. Exemplary semiconducting polymers include, but are not limited to, poly(3-hexylthiophene)(P3HT), poly[(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)-benzo[1,2-b:4,5-b′]dithiophene))-alt-(5,5-(1′,3′-di-2-thienyl-5′,7′-bis(2-ethylhexyl)benzo[1′,2′-c:4′,5′-c′]dithiophene-4,8-dione)])(PBDB-T), poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine](PTAA), poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene](MEH-PPV), poly[4,8-bis-(2-ethyl-hexyl-thiophene-5-yl)-benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl]-alt-[2-(2′-ethyl-hexanoyl)-thieno[3,4-b]thiophen-4,6-diyl](PBDTTT-CT), poly[N-9′-hepta-decanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-enzothiadiazole)](PCDTBT), poly[6-fluoro-2,3-bis-(3-octyloxyphenyl) quinoxaline-5,8-diyl-alt-thiophene-2,5-diyl](FTQ), poly(3-octylthiophene) (P3 T), poly(3-hexyloxythiophene)(P3DOT), poly(3-methylthiophene)(PMeT), poly(3-dodecylthiophene)(P3DDT), poly(3-dodecylthienylenevinylene)(PDDTV), poly(3,3 dialkylquarterthiophene)(PQT), poly-dioctyl-fluorene-co-bithiophene (F8T2), Poly[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]](PTB7), poly-(2,5,-bis(3-alkylthiophene-2-yl)thieno[3,2-b]thiophene)(PBTTT-C12), poly[2,7-(9,9′-dihexylfluorene)-alt-2,3-dimethyl-5,7-dithien-2-yl-2,1,3-benzothiadiazole](PFDDTBT), poly{[2,7-(9,9-bis-(2-ethylhexyl)-fluorene)]-alt-[5,5-4,7-di-20-thienyl-2,1,3-benzothiadiazole)]} (BisEH-PFDTBT), poly{[2,7-(9,9-bis-(3,7-dimethyl-octyl)-fluorene)]-alt-[5,5-(4,7-di-20-thienyl-2,3-benzothiadiazole)]} (BisDMO-PFDTBT), poly[N-9″-hepta-decanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)](PCDT3BT), poly[4,8-bis-substituted-benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl-alt-4-substituted-thieno[3,4-b]thio-phene-2,6-diyl](PBDTTT-C-T), Poly(benzo[1,2-b:4,5-b′]dithiophene-alt-thieno[3,4-c]pyrrole-4,6-dione (PBDTTPD), poly((4,4-dioctyldithieno(3,2-b:2′,3′-d)silole)-2,6-diyl-alt-(2,1,3-benzothiadiazole)-4,7-diyl)(PSBTBT), poly[4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b; 4,5-b′]dithiophene-2,6-diyl-alt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene-)-2-carboxylate-2-6-diyl)](PTB7-Th), poly[(5,6-difluoro-2,1,3-benzothiadiazol-4,7-diyl)-alt-(3,3′″-di(2-octyldodecyl)-2,2′,5′,2″,5″,2′″-quaterthiophen-5,5′″-diyl)](PffBT4T-2OD), poly[(2,5-bis(2-hexyldecyloxy)phenylene)-alt-(5,6-difluoro-4,7-di(thiophen-2-yl)benzo[c]-[1,2,5]thiadiazole)](PPDT2FBT), Poly[2-(5-(4,8-bis(5-((2-butyloctyl)thio)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophen-2-yl)-4-octylthiophen-2-yl)-5-(4-octylthiophen-2-yl)-1,3,4-thiadiazole](PBDTS-TDZ), Poly[2,5-(2-decyltetradecyl)-3,6-diketopyrrolopyrrole-alt-5,5-(2,5-di(thien-2-yl)thieno[3,2-b]thiophene)](PDPPTT), Poly[2,5-(2-octyldodecyl)-3,6-diketopyrrolopyrrole-alt-5,5-(2,5-di(thien-2-yl)thieno[3,2-b]thiophene)](PDPP2T-TT-OD), and poly{1-(5-(4,8-bis((2-ethylhexyl)oxy)-6-methylbenzo[1,2-b:4,5-b0]dithiophen-2-yl)thiophen-2-yl)-5,7-bis-(2-ethylhexyl)-3-(5-methylthiophen-2-yl)benzo[1,2-c:4,5-c0]dithiophene-4,8-dione} (PDBD-O), poly(benzimidazobenzophenanthroline), diphenyl terminated poly[(2,5-didecyloxy-1,4-phenylene)(2,4,6-triisopropylphenylborane)], poly(2,5-di(3,7-dimethyloctyloxy)cyanoterephthalylidene), poly(2,5-di(hexyloxy)cyanoterephthalylidene), poly(5-(3,7-dimethyloctyloxy)-2-methoxy-cyanoterephthalylidene), poly(2,5-di(octyloxy)cyanoterephthalylidene), poly(5-(2-ethylhexyloxy)-2-methoxy-cyanoterephthalylidene), and the like.

In one embodiment, the step of contacting the organic semiconductor solution with COcomprises the step of contacting the solution with solid CO(“dry ice”). For example, some quantity of dry ice may be added to the solution. In one embodiment, the solution is permitted to warm, thereby causing the release COgas.

In one embodiment, the step of contacting the organic semiconductor solution with COcomprises the step of carbonating the solution. In one embodiment, the solution may be carbonated with any device or instrument capable of introducing COinto a solution with concommitant pressurization of the system. In one embodiment, the pressure within the system comprising the solution may be maintained for any period of time and at any pressure or temperature. In one embodiment, the solution is depressurized, such as by opening the system to atmospheric conditions.

In one embodiment, the step of contacting the organic semiconductor solution with COcomprises the step of bubbling COgas through the semiconductor solution. For example, a gas outlet may be positioned outside the solution, such as in a “head space” of a reaction vessel, and a gas inlet may be immersed in the solution, or otherwise placed in such as a way as to permit transit of gas through the solution. There is no particular limit to the duration of the CObubbling treatment. Said duration may be tuned depending on the concentration of the organic semiconductor solution, the components, the solvent identity, the volume of solvent, and any other factors affecting diffusion (such as stir rate, etc.). Similarly, there is no particular limit to the rate of CObubbling, which may depend on the COsource utilized. In one embodiment, the COis bubbled at a rate of about 2 mL/min. In one embodiment, the solution is bubbled with COfor about 1 minute. In one embodiment, the solution is bubbled with COfor greater than 1 minute.

The apparatus used for bubbling COcan be any apparatus known to those of skill in the art. In one embodiment, the step of contacting the organic semiconductor solution with COis performed in a COatmosphere. In one embodiment, the COcontent of ambient air is not sufficient to cause the inventive effects. In one embodiment, the COcontent of exhaled air is not sufficient to cause the inventive effects. In one embodiment, the COcontent of the gas is at least about 5%, at least about 10%, at least about 15%, at least about 20%, at least about 25%, at least about 30%, at least about 35%, at least about 40%, at least about 45%, at least about 50%, at least about 55%, at least about 60%, at least about 65%, at least about 70%, at least about 75%, at least about 80%, at least about 85%, at least about 90%, at least about 95%, or about 100%. In one embodiment, the COgas further comprises one or more additional gases, such as but not limited to nitrogen, oxygen, hydrogen, helium, and argon.

In one embodiment, Ogas may be bubbled instead of COgas.

In one embodiment, the irradiation with ultraviolet (UV) light may be performed using any method known in the art, for example, by a method using a low-pressure mercury lamp, a high pressure mercury lamp, a mercury-xenon lamp, a UV laser or otherwise focused beam device, or the like. In one embodiment, the UV light has a wavelength between about 100 nm and about 400 nm. In one embodiment, the UV light has a wavelength between about 100 nm and about 280 nm. In one embodiment, the UV light has a wavelength between about 280 nm and about 315 nm. In one embodiment, the UV light has a wavelength between about 315 nm and about 400 nm. In one embodiment, the UV light has a wavelength of about 365 nm.

In some embodiments, the step of irradiating the solution with UV light comprises the step of irradiating the solution with visible light. In one embodiment, the light has a wavelength between 380 nm and 450 nm. In one embodiment, the light has a wavelength between 400 nm and 700 nm. In one embodiment, the light has a wavelength between 450 nm and 495 nm. In one embodiment, the light has a wavelength between 495 nm and 570 nm. In one embodiment, the light has a wavelength between 570 nm and 590 nm. In one embodiment, the light has a wavelength between 590 nm and 620 nm. In one embodiment, the light has a wavelength between 620 nm and 750 nm.

In some embodiments, the step of irradiating the solution with UV light further comprises the step of identifying the ideal absorption wavelength for the organic semiconductor. In one embodiment, the absorption wavelength for a particular organic semiconductor may be determined using methods generally known to those of skill in the art. However, the wavelength of light with which the organic semiconductor is irradiated is not limited to the absorption wavelength thus determined. In one embodiment, wavelength of light corresponds to the energy greater than the band gap of the organic semiconductor.

In one embodiment, the organic semiconductor solution comprises an organic solvent. Exemplary solvents include, but are not limited to, water, methanol, ethanol, 1-pronanol, 2-propanol, n-butanol, 1-pentanol, t-butyl alcohol, carbon tetrachloride, chlorobenzene, dichlorobenzene (ortho-, meta-, or para-), ethylbenzene, ortho-, meta- or para-xylene, ethyl acetate, acetone, dichloromethane, chloroform, benzene, toluene, ethylene glycol, pentane, hexane, petroleum ether, diethyl ether, acetic acid, acetonitrile, 1,2-dimethoxyethane, dimethylformamide, dimethyl sulfoxide, 1,4-dioxane, n-methyl-2-pyrrolidinone, nitromethane, pyridine, tetrahydrofuran, triethylamine, quinoline, cumene, high boiling ethers, gamma butyrolactone, ethyl lactate, methyl 2-hydroxyisobutyrate, PGMEA, cyclohexanone, tetrahydrofurfuryl alcohol, propylene carbonate, 2-heptanone, NMP, diacetone alcohol, ionic liquids, glycerin, and combinations thereof. In one embodiment, the solvent comprises chlorobenzene, dichloromethane, chloroform, or carbon tetrachloride.

In one embodiment, the bubbling of COand/or irradiation with UV light is performed at room temperature. In one embodiment, the bubbling of COand/or irradiation with UV light is performed at elevated temperature (i.e., greater than room temperature). In one embodiment, the bubbling of COand/or irradiation with UV light is performed at decreased temperature (i.e., lower than room temperature).

In one embodiment, the method further comprises step, in which at least one precipitate is removed from the organic semiconductor solution. Precipitates may be removed using any method known in the art, including but not limited to vacuum filtration and centrifugation. In one embodiment, the method does not include the step of removing a precipitate. In one embodiment, the precipitate comprises a carbonate salt or a bicarbonate salt. In one embodiment, the precipitate comprises LiCO. In one embodiment, the precipitate comprises carbon. In one embodiment, the precipitate comprises one or more additional carbon-containing species.

In one embodiment, the method further comprises step, in which a doped organic semiconductor material is isolated from the solution. In one embodiment, said step comprises the step of pouring the organic semiconductor solution into a second solvent, such as a solvent in which the organic semiconductor is sparingly soluble or insoluble. In one embodiment, the isolation step affords a mixture of doped and non-doped semiconductor. In one embodiment, solvent in which the organic semiconductor is dissolved is at least partially miscible in the second solvent Exemplary solvents may include hexanes, pentane, benzene, alkylbenzenes (i.e, toluene and the like), diethyl ether, methyl tert-butyl ether (MTBE), and any other solvent disclosed herein or known in the art. The solid precipitate can then be filtered from the second solvent using any method known to those of skill in the art.

In one aspect, the present invention relates to a composition comprising: an organic semiconductor; and a metal salt having the formula MX; wherein Xis a monoanionic species; and wherein the ratio of Mto Xin the hole transport material is less than about 1.00.

In another aspect, the present invention relates to a composition comprising an organic semiconductor; a metal salt having the formula MXwherein Xis a monoanionic species; and a metal carbonate having the formula MCO, where the M of the metal salt and the M of the carbonate is the same metal; wherein the total metal content (M) of the composition is approximately equal to the Xcontent of the composition. In one embodiment, the metal is Li and the carbonate is lithium carbonate.

In some embodiments, the composition of the invention may be a doped hole transport material. In one embodiment, the composition comprises at least one small molecule semiconductor. In one embodiment, the small molecule semiconductor comprises a mixture of ground state compounds and excited state compounds, such as excited derivatives of the ground state compounds. In one embodiment, the excited state compounds include radical cations and diradical-dications. In one embodiment, the small molecule semiconductor comprises spiro-OMeTAD or any derivative thereof. In one embodiment, the small molecule semiconductor comprises spiro-OMeTAD′. In one embodiment, the small molecule semiconductor comprises spiro-OMeTAD″. In one embodiment, the radical cations and diradical dications comprise stabilizing anion(s), such as TFSI, in a proportion so as to render the overall complex neutral.